CN105545498B - Method and system for engine temperature control - Google Patents

Abstract

The invention relates to a method and a system for engine temperature control. Methods and systems are provided for improved engine temperature control. A cylinder scheduled for deactivation may have its exhaust held in the cylinder by holding the exhaust valve closed during a previous ignition cycle. In this way, soot emissions upon reactivation are reduced.

Description

Method and system for engine temperature control

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to US Provisional Patent Application No. 62/067,354, filed October 22, 2014, entitled "METHOD AND SYSTEM FOR ENGINE TEMPERATURE CONTROL," and for all purposes, Its entire contents are incorporated herein by reference.

technical field

The present application relates to methods and systems for maintaining engine temperature and/or exhaust catalyst temperature to control particulate matter emissions from an engine system configured to perform skip-ignition combustion.

Background technique

After an engine cold start, exhaust emissions and fuel consumption tend to be higher. This is because a cold combustion surface results in poor fuel evaporation, resulting in a fuel film that exists on the combustion surface even after a combustion event has occurred. Fuel-rich regions above the membrane and fuel vaporized from the membrane after the flame has dissipated can lead to increased hydrocarbon and particulate matter (PM) emissions. Furthermore, cold engine oil results in increased frictional losses.

In recent years, spark ignition combustion engines have been configured to operate with a variable number of cylinders activated or deactivated to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio at stoichiometric than nearby. Such engines are capable of changing the effective displacement of the engine by skipping the delivery of fuel to certain cylinders in an indexed cylinder firing mode (also known as a "skip fire" mode). For example, as shown by Tripath et al in US 8,651,091, the engine fuel controller may continuously rotate which particular cylinders are fueled, which cylinders are skipped, and for how many cylinder events the mode is continued. Additionally, individual valve trains for each cylinder may be selectively deactivated. By skipping fuel delivery to selected cylinders, the activated cylinders are able to operate near their optimum efficiency, thereby increasing the overall operating efficiency of the engine.

SUMMARY OF THE INVENTION

The inventors herein have recognized that individually controllable valves for selectively deactivated cylinders can be used to improve the rate at which cylinders warm up during a drive cycle. Specifically, valve operation of cylinders that will not be fired in the next cycle due to engine load may be controlled to keep hot exhaust gas in the cylinders, thereby heating the combustion chamber surfaces faster. In one example, some of the above problems may be addressed by a method of increasing the rate at which the engine warms up during cylinder deactivation, the method comprising: selecting cylinders for deactivation; and a combustion cycle immediately prior to deactivation , maintaining the exhaust valve of the selected cylinder closed during the cylinder's exhaust stroke. In this way, fast-response individual cylinder valve trains can be used to increase combustion surface temperatures.

As an example, in response to a drop in engine load, the engine controller may select cylinder modes for individual cylinders of the mechanism for selective deactivation. Among other things, the controller may select the number and identification of the cylinders to be deactivated. Cylinders that are selected for deactivation and will not be fired for the next engine cycle may have their exhaust valves held closed during the exhaust stroke of the firing cycle immediately prior to deactivation. Specifically, instead of exhausting the combusted gases, the hot gases are kept in the cylinder by not opening the exhaust valve. Exhaust gas is then held in the cylinder, which is deactivated on the next cycle.

In this way, the combustion chamber surfaces are heated faster by keeping the hot exhaust gas in the cylinder for the next cycle. Thus, the entire engine is also heated faster. Additionally, maintaining the combusted gases in the deactivated cylinders longer improves the continued oxidation of hydrocarbons remaining in the combustion chambers, resulting in improved emissions for the cycle. Overall, engine performance is improved.

Other valve operations can still be used in various combinations to improve engine heating and allow for accelerated catalyst warming. For example, the cylinders to be deactivated may be normally fired and normally exhausted for the engine cycle prior to deactivation. Alternatively, the cylinders may be configured to draw in air but not fuel, and discharge fresh charge. In yet another example, the cylinders may draw in air and fire, but not exhaust. By deciding to take in and pass air, the expelled air can mix with exhaust from other cylinders operating slightly richer to provide fuel and air at the exhaust catalyst. The reaction of fuel and air at the exhaust catalyst generates heat that results in rapid catalyst light-off. Other alternatives may include sucking in air and supplying fuel without misfiring during the intake or compression stroke to provide a fuel-air mixture to the catalyst. Additionally, air may be drawn into the cylinder, compressed, but not fueled, until the exhaust stroke, ie, as a post injection. The latter method may also include ignition near the exhaust stroke and combustion into the exhaust phase to provide heat flux to the exhaust catalyst. In this way, various combinations of firing, misfiring, firing during post injection, rich operation in some cylinders while pumping air with other cylinders, etc., may be used in various combinations, while in such a manner Known torque pulses are introduced into the engine system in order to provide acceptable NVH characteristics. Additionally, cylinders that are already firing normally (active cylinders) can be operated at higher loads, making them more stable and more tolerant of additional spark retard. Additional spark retard can be used advantageously to add more heat flux to the engine and exhaust catalyst under these conditions.

It should be understood that the above summary is provided to introduce some concepts in a simplified form that are further described in the Detailed Description. This is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims appended to the Detailed Description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

Description of drawings

FIG. 1 shows an example embodiment of an engine system layout.

Figure 2 shows a partial view of the engine.

3 shows a high-level flow diagram for adjusting cylinder valve operation to accelerate engine heating during and before cylinder deactivation.

FIG. 4 illustrates example cylinder valve adjustments to reduce PM emissions during a transition to a skip-fire operating mode.

Detailed ways

Methods and systems are provided for adjusting cylinder valve profiles when operating an engine, such as the engine system of FIGS. 1-2 , configured for selective cylinder deactivation (also referred to herein as skip-fire operation) . A controller may adjust operation of exhaust valves of cylinders selected for selective deactivation. For example, the controller may execute a routine, such as the example routine of FIG. 3 , to keep the exhaust valves of cylinders to be deactivated for subsequent engine cycles closed. By keeping hot exhaust gas in the cylinder during deactivation, the compression surface temperature can be raised, thereby speeding up engine heating. An example adjustment is shown with reference to FIG. 4 . In this manner, particulate matter emissions from cold cylinders may be reduced.

FIG. 1 shows an example engine 10 having a first cylinder bank 15a and a second cylinder bank 15b. In the depicted example, engine 10 is a V8 engine with first and second cylinder banks, each having four cylinders. Engine 10 has intake manifold 16 with throttle 20 and exhaust manifold 18 coupled to emission control system 30 . Emission control system 30 includes one or more catalysts and an air-fuel ratio sensor such as those described with respect to FIG. 2 . As one non-limiting example, engine 10 can be included as part of a propulsion system for a passenger vehicle.

Engine system 10 may have cylinder 14 with selectively deactivatable intake valve 50 and selectively deactivatable exhaust valve 56 . In one example, intake valve 50 and exhaust valve 56 are configured for electronic valve actuation (EVA) via electronic individual cylinder valve actuators. Although the described example shows a single intake valve and a single exhaust valve per cylinder, in alternative examples, as detailed at FIG. 2 , each cylinder may have multiple selectively deactivatable intake valve and/or multiple selectively deactivatable exhaust valves.

During selected conditions, such as when the full torque capacity of the engine is not required, one or more cylinders of engine 10 may be selected for selective deactivation (also referred to herein as individual cylinder deactivation). This may include selectively deactivating only one or more cylinders on the first cylinder bank 15a, only one or more cylinders on the second cylinder bank 15b, or each of the first and second cylinder banks One or more cylinders on a cylinder bank. The number and identification of deactivated cylinders on each cylinder bank may be symmetrical or asymmetrical.

During deactivation, selected cylinders may be deactivated by closing individual cylinder valve trains, such as intake valve trains, exhaust valve trains, or a combination of both. Cylinder valves may be via hydraulically actuated tappets (eg, tappets coupled to valve lifters), via cam lobes with no lift, cam profile shifting mechanisms for deactivated valves, or via coupling The electrically actuated cylinder valve trains connected to each cylinder are selectively deactivated. Additionally, fuel flow and spark to deactivated cylinders may be stopped, such as by deactivating cylinder fuel injectors.

In some examples, engine system 10 may have selectively deactivatable (direct) fuel injectors, and selected cylinders may be deactivated by shutting off corresponding fuel injectors while maintaining operation of the intake and exhaust valves , so that air can continue to be pumped through the cylinder.

While the selected cylinder is disabled, the remaining enabled or activated cylinders continue to perform combustion with fuel injectors and cylinder valve trains activated and operating. To meet the torque request, the engine produces the same amount of torque on the activated cylinders. This requires higher manifold pressure, resulting in lower pumping losses and increased engine efficiency. Also, the lower effective surface area exposed to combustion (from only activated cylinders) reduces engine heat loss, thereby improving engine thermal efficiency.

Cylinders may be deactivated to provide specific firing (or skip firing) patterns based on specified control algorithms. More specifically, selected "jumped" duty cycles are not fired, while other "active" duty cycles are fired. Optionally, the spark timing associated with the selected firing of the selected working chamber may also be adjusted based on the firing order or firing history of the selected working chamber. The engine controller 12 may be configured with suitable logic for determining the cylinder deactivation (or skip fire) mode based on engine operating conditions, as described below.

Engine 10 may operate with a variety of substances that may be delivered via fuel system 8 . Engine 10 may be at least partially controlled by a control system including controller 12 . The controller 12 may receive various signals from sensors 17 coupled to the engine 10 (and described with reference to FIG. 2 ) and to various actuators 81 coupled to the engine and/or the vehicle (and described with reference to FIG. 2 ) Send control signals. The various sensors may include, for example, various temperature, pressure, and air-fuel ratio sensors.

The engine controller may include a drive pulse generator and sequencer for determining a cylinder mode based on a desired engine output under current engine operating conditions. For example, the drive pulse generator may use adaptive predictive control to dynamically calculate drive pulse signals that indicate which cylinders are to be fired and at what intervals to achieve the desired output (ie, cylinder firing/skip firing patterns). Cylinder firing patterns may be adjusted to provide the desired output without creating excessive or undue vibration within the engine. Thus, the cylinder mode may be selected based on the configuration of the engine (such as based on whether the engine is a V-engine, an inline engine, the number of engine cylinders present in the engine, etc.). Based on the selected cylinder mode, individual cylinder valve trains for the selected cylinder may be closed while fuel flow and spark to that cylinder are stopped.

Since the optimum efficiency for a given cylinder is nearly full output, lower frequency firing events can be selected to reduce output. For example, on average, jumping every other cylinder will produce half the power. Spaced out firing events as evenly as possible tends to minimize vibration due to varying torque output. Whether or not all cylinders are included, the skip fire mode may depend on the desired output fraction, other considerations including cylinder temperature.

In this way, by adjusting the cylinder patterns of individual cylinder valve trains and individual cylinder fuel injectors, desired engine output can be provided by operating fewer cylinders more efficiently, thereby improving fuel economy.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinder of internal combustion engine 10 . Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132 . In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinders (also referred to herein as "combustion chambers") 14 of engine 10 may include combustion chamber walls 136 in which pistons 138 are disposed. Piston 138 may be coupled to crankshaft 140 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Additionally, a starter motor may be coupled to crankshaft 140 via a flywheel to enable starting operation of engine 10 .

Cylinder 14 can receive intake air via a series of intake air passages 142 , 144 and 146 . Intake air passage 146 may communicate with other cylinders of engine 10 other than cylinder 14 . In some embodiments, one or more of the intake passages may include a boost device, such as a turbocharger or supercharger. For example, FIG. 2 shows engine 10 configured with a turbocharger including compressor 174 disposed between intake passages 142 and 144 and exhaust turbine 176 disposed along exhaust passage 148 . Exhaust turbine 176 may at least partially power compressor 174 via shaft 180 , in which case the booster device is configured as a turbocharger. However, in other examples, such as where engine 10 is equipped with a supercharger, exhaust turbine 176 may optionally be omitted, in which case compressor 174 may be provided by mechanical input from a motor or engine power. A throttle 20 including a throttle plate 164 may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, as shown in FIG. 2 , throttle 20 is disposed downstream of compressor 174 , or alternatively, may be provided upstream of compressor 174 .

Exhaust passage 148 may receive exhaust gas from cylinders other than cylinder 14 of engine 10 . Exhaust gas oxygen sensor 128 is shown coupled to exhaust passage 148 upstream of emission control device 178 . Sensor 128 may be selected from a variety of suitable sensors for providing an indication of exhaust air-fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as shown) , HEGO (Heated EGO), NOx, HC or CO sensors. Emission control device 178 may be a three-way catalyst (TWC), NOx trap, various other emission control systems, or combinations thereof.

Exhaust temperature may be measured by one or more temperature sensors (not shown) located in exhaust passage 48 . Alternatively, the exhaust gas temperature may be inferred based on engine operating conditions (eg, speed, load, air-fuel ratio (AFR), spark retard, etc.). Additionally, exhaust gas temperature may be calculated by one or more exhaust gas oxygen sensors 128 . It will be appreciated that exhaust temperature may alternatively be estimated by any combination of the temperature estimation methods listed herein.

Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located in an upper region of cylinder 14 . In some embodiments, each cylinder of engine 10 (including cylinder 14 ) may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 through cam actuation system 151 . Similarly, exhaust valve 156 may be controlled by controller 12 through cam actuation system 153 . Cam actuation systems 151 and 153 may each include one or more cams, and may use cam profile switching (CPS), variable cam timing (VCT), variable valve timing ( VVT) and/or one or more of variable valve lift (VVL) systems to vary valve operation. Operation of intake valve 150 and exhaust valve 156 may be determined by valve position sensors (not shown) and/or crankshaft position sensors 155 and 157 , respectively. In alternative embodiments, the intake and/or exhaust valves may be controlled by electric valve actuation. For example, cylinder 14 may alternatively include intake valves controlled via electric valve actuation and exhaust valves controlled via cam actuation including CPS and/or VCT systems. In another embodiment, the intake and exhaust valves may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system.

Cylinder 14 can have a compression ratio, which is the ratio of the volume of piston 138 at top dead center to bottom dead center. Typically, the compression ratio is in the range of 9:1 to 13:1. However, in some examples using different fuels, the compression ratio may be increased. This can occur, for example, when using higher octane fuels or fuels with higher potential enthalpy of vaporization. If direct injection is used, the compression ratio can also be increased due to its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. In the selected operating mode, ignition system 190 can provide an ignition spark to combustion chamber 14 via spark plug 192 in response to spark advance signal SA from controller 12 .

In some embodiments, each cylinder of engine 10 may be configured with one or more injectors for delivering fuel to the cylinder. As one non-limiting example, cylinder 14 is shown including two fuel injectors 166 and 170 . Fuel injectors 166 and 170 may be configured to deliver fuel received from fuel system 8 via a fuel pump and a fuel rail above. Alternatively, fuel is delivered at a lower pressure by a single stage fuel pump, in which case the timing of direct fuel injection may be more limited during the compression stroke than if a high pressure fuel system is used. Additionally, the fuel tank may have a pressure sensor that provides a signal to the controller 12 .

Fuel injector 166 is shown coupled directly to cylinder 14 for injecting fuel directly into the cylinder via electronic driver 168 in proportion to the pulse width of signal FPW- 1 received from controller 12 . In this manner, fuel injector 166 provides so-called direct injection of fuel (hereinafter referred to as “DI”) into combustion cylinder 14 . Although FIG. 2 shows injector 166 disposed on one side of cylinder 14 , it may instead be located on top of the piston, such as near spark plug 192 . This location can improve mixing and combustion when running the engine on alcohol-based fuels due to the lower volatility of some alcohol-based fuels. Alternatively, the injector can be located at the top and close to the intake valve to improve mixing.

Fuel injector 170 is shown arranged in intake passage 146 , rather than in cylinder 14 , in a configuration that provides so-called port injection of fuel (hereinafter referred to as the intake port) into the intake port upstream of cylinder 14 . as "PFI"). Fuel injector 170 may inject fuel received from fuel system 8 in proportion to the pulse width of signal FPW- 2 received from controller 12 via electronic driver 171 . Note that a single driver 168 or 171 may be used for both fuel injection systems, or multiple drivers may be used as described (eg, example driver 168 for fuel injector 166 and driver 171 for fuel injector 170 ) .

Fuel injectors 166 and 170 may have different characteristics. These include differences in size, eg, one injector may have a larger orifice than another. Other differences include, but are not limited to, different spray angles, different operating temperatures, different targets, different spray timing, different spray characteristics, different locations, and the like. Also, depending on the distribution ratio of the injected fuel between injectors 170 and 166, different effects may be achieved.

During a single cycle of the cylinder, fuel may be delivered to the cylinder through two injectors. For example, each injector may deliver a portion of the total fuel injection combusted in cylinder 14 . Thus, even for a single combustion event, the fuel to be injected may be injected at different timings from the port and direct injectors. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. Multiple injections may be performed during the compression stroke, the intake stroke, or any suitable combination thereof.

As described above, FIG. 2 shows only one cylinder of a multi-cylinder engine. Likewise, each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plugs, and the like. It should be appreciated that engine 10 may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Additionally, each of these cylinders can include some or all of the various components described and depicted with reference to cylinder 14 through FIG. 2 .

The engine may further include one or more exhaust gas recirculation passages for recirculating a portion of the exhaust gas from the engine exhaust to the engine intake. Thus, by recirculating some of the exhaust gas, engine dilution can be affected, which can improve engine performance by reducing engine knock, peak cylinder combustion temperatures and pressures, throttling losses, and NOx emissions. In the depicted embodiment, exhaust gas may be recirculated from exhaust passage 148 to intake passage 144 via EGR passage 141 . The amount of EGR provided to intake passage 144 may be varied by controller 12 via EGR valve 143 . Additionally, an EGR sensor 145 may be disposed within the EGR passage and may provide an indication of one or more of the pressure, temperature, and concentration of the exhaust gas.

The controller 12 is shown in FIG. 2 as a microcomputer that includes a microprocessor unit (CPU) 106, input/output ports (I/O) 108, in this particular example as a read only memory chip (ROM) 110. An electronic storage medium for executable programs and calibration values, a random access memory (RAM) 112, a keep-alive accessor (KAM) 114, and a data bus are provided. The controller 12 may receive various signals from sensors coupled to the engine 10 , including, in addition to those previously discussed, a measurement of the introduced mass air flow (MAF) from the mass air flow sensor 122 ; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; surface ignition sense signal (PIP) from Hall effect sensor 120 (or other type) coupled to crankshaft 140; throttle position (TP) from the valve position sensor; and manifold absolute pressure signal (MAP) from sensor 124 . Engine speed signal RPM may be generated by controller 12 from signal PIP. The manifold pressure signal MAP from the manifold pressure sensor may be used to provide an indication of vacuum or pressure within the intake manifold. Other sensors may include a fuel level sensor and a fuel composition sensor coupled to the fuel tank(s) of the fuel system.

Storage medium read-only memory 110 can be programmed with computer-readable data representing instructions executable by processor 106 for performing the methods described below and other variants that are desired but not specifically listed. The controller 12 receives signals from the various sensors of FIGS. 1-2 and employs the various actuators of FIGS. 1-2 to adjust engine operation based on the received signals and instructions stored on the controller's memory.

In this manner, the system of FIGS. 1-2 implements a method for an engine comprising: selecting a cylinder for deactivation; and maintaining all of the cylinders during the exhaust stroke of the combustion cycle immediately prior to deactivation The exhaust valve of the selected cylinder is closed. In one example, the selected cylinder is the first cylinder, the method further includes selecting a second, different cylinder for deactivation, and the combustion cycle immediately preceding the deactivation, opening during the exhaust stroke of the second cylinder Close the exhaust valve of the second cylinder. Deactivation may be performed in response to a drop in engine load. The maintenance is performed after the exhaust gas temperature is higher than the threshold temperature.

In another example, a method for an engine includes deactivating a cylinder mode of an individual cylinder mechanism, the cylinder mode including a first deactivated cylinder and a second activated cylinder, wherein in response to a first deactivated cylinder Deactivation of the cylinder is commanded, the exhaust valve of the first cylinder is held closed for the exhaust stroke of the ignition cycle immediately prior to the deactivation of the first cylinder.

FIG. 3 shows an example of a routine 300 for adjusting individual cylinder valve trains in response to engine temperature, exhaust gas temperature, and/or exhaust catalyst temperature during cylinder deactivation. This method allows exhaust gas to be trapped in deactivated cylinders, thereby maintaining the combustion surfaces of the cylinders hot during deactivation. By reducing cooling of deactivated cylinders, the frequency of cylinder reactivation is reduced while also reducing PM emissions from reactivated cylinders. Instructions for performing method 300 may be executed by a controller based on instructions stored on a memory of the controller in conjunction with signals received from sensors of the engine system, such as those described above with reference to FIGS. 1-2 . The controller may employ engine actuators of the engine system, such as the actuators described with reference to FIGS. 1-2 , to adjust engine operation according to the methods described below.

At 302 , the routine includes estimating and/or measuring engine operating conditions. Estimated conditions may include, for example, engine speed, driver torque demand, engine temperature, ambient conditions (such as ambient temperature, humidity, and barometric pressure), boost levels, and the like. At 304 , based on the estimated conditions, it may be determined whether cylinder deactivation conditions have been met. In one example, a cylinder deactivation condition may be considered satisfied if the engine load is below a threshold, or if the driver torque demand is below a threshold. If the cylinder deactivation conditions are not met, then at 305 the routine includes maintaining activation of all engine cylinders.

If the cylinder deactivation conditions are met, then at 306 , the controller may select the cylinder mode based on engine load. The cylinder deactivation mode may be selected based on engine speed, vehicle speed, engine temperature, engine NVH, and transmission gear selection (eg, whether the engine is currently in a first transmission gear with a first lower gear ratio or a second higher gear ratio). One or more of the gear ratios (second transmission gears) are further selected. Determining the cylinder mode includes determining the number and identification of cylinders to be deactivated, and further determining a duration of deactivation. For example, the controller may determine the number of combustion events or engine cycles during which the selected cylinders are maintained deactivated. The total number of deactivated/activated cylinders may depend on the total actual number of engine cylinders and driver demand torque. As non-limiting examples, two cylinders may be deactivated for a four-cylinder engine, three cylinders may be deactivated for a six-cylinder engine, and four cylinders may be deactivated for an eight-cylinder engine. In some examples, the same group of cylinders may be selected for deactivation whenever a cylinder deactivation condition is met, while in other examples, whenever a cylinder deactivation condition is met, the deactivated cylinder's The logo can be changed.

As an example, the controller may retrieve the schema from a look-up table stored in the controller's memory. The cylinder mode may be stored in a look-up table as a function of engine load for a given engine configuration. In one example, at lower engine loads, the cylinder mode may include firing of each of the second or third cylinders. As an example, in an inline four-cylinder engine with cylinders labeled 1 through 4 and having a cylinder firing pattern of 1-3-4-2, under normal operating conditions, when no cylinders are deactivated and all When both cylinders are activated, the cylinders can fire at 134213421342 etc. In response to the cylinder deactivation condition being met, to provide fuel economy benefits, the controller may transition engine operation to a cylinder mode where each third cylinder is fired resulting in mode 1xx2xx4xx3xx1xx, where x represents the skipped cylinder.

At 308 , it may be determined whether cylinder cooling or engine cooling is desired. In one example, when the engine is operating at a low to very light engine load for an extended amount of time (eg, allowing longer than a threshold duration at a load below a threshold, or longer than a threshold duration with cylinder deactivation), Some engine cooling can be expected. In another example, engine cooling may be desired if the vehicle is traveling on a road with a negative gradient (ie, traveling downhill). In another example, engine cooling may be desired if the ambient temperature is low. As yet another example, engine cooling may occur if the engine temperature is relatively low and a tip-out event occurs. Therefore, engine cylinder cooling can result in degraded exhaust emissions when the cylinders are subsequently reactivated. Also, fuel consumption will be higher when operating with cooler cylinders. If cylinder cooling is not desired, then at 310 the routine includes transitioning to operating the engine in the cylinder mode determined at 306 .

If cylinder cooling is desired, then at 312 it may first be determined whether the exhaust temperature is hot enough. Specifically, it can be confirmed that the exhaust gas temperature is higher than a threshold value that provides light-off of the exhaust catalyst. If the exhaust gas temperature is not hot enough, at 313 , the routine includes retarding cylinder deactivation until the exhaust gas temperature is hot enough. This delay allows particulate matter emissions due to combustion surface cooling to be reduced.

It will be appreciated, however, that in some examples, the controller may proceed to 314 to deactivate one or more engine cylinders even when the exhaust gas temperature is below a threshold, while relying on the descriptions described herein at 318 Additional cylinder valve adjustment to increase exhaust temperature and accelerate catalyst light-off. In this way, cylinder deactivation benefits can be realized for longer durations of engine operation.

Returning to 312 , if the exhaust temperature is hot enough, then at 314 the routine includes identifying one or more cylinders to be deactivated in the next engine cycle (eg, based on the cylinder mode selected at 306 ). That is, the first cylinder that fires in the current cycle but will not fire in the next cycle may be identified based on engine load. The first cylinder may be different from the second cylinder (active engine cylinder) that fires in each of the current cycle and the next cycle. At 316 , the identified cylinder(s) are operating for the current cycle with the exhaust valve maintained closed on the exhaust stroke. That is, instead of venting the combusted gases and leaving the cylinder motor with very little charge or fresh air for the next cycle, the burned gases are retained by not opening the exhaust valve after combustion in the cylinder and until the cylinder is reactivated in the cylinder. By keeping hot exhaust gas in the cylinder during the next cycle (when the cylinder is deactivated), the combustion chamber surfaces of a given cylinder can remain hot longer. By similarly performing exhaust valve deactivation on one or more other cylinders scheduled to be deactivated, cylinder heating can be achieved even when the cylinder is deactivated. Thus, this allows the engine to be gradually heated. By keeping the combusted gases in the cylinder for a longer duration, the continued oxidation and exhaust of the hydrocarbons held in the chamber is also improved, resulting in improved emissions for the cycle.

In one example, determining the selected cylinder mode includes determining that the selected cylinder(s) are to be deactivated over a number of engine cycles. Therein, maintaining the exhaust valve of the selected cylinder closed in response to the number of engine cycles being above a threshold number of times. For example, when the number of engine cycles is above a threshold number, deactivation can result in significant cylinder cooling, which can require more fuel during subsequent reactivations. The threshold number may be based on one or more of engine coolant temperature, ambient temperature, and cylinder temperature, the threshold number decreasing as any one of engine coolant temperature, ambient temperature, and cylinder temperature decreases. Here, by keeping the exhaust valve closed, more heat is retained in the cylinder to be deactivated, and for a longer time, thereby reducing the deactivated cylinder cooling effect.

It should be appreciated that when a given cylinder is subsequently reactivated, the exhaust valve(s) of the reactivated cylinder may be opened before the intake valve(s) are opened to allow the trapped cylinders to remain Any residual gas is pushed out before fresh charge is drawn into the cylinder. This allows the occurrence of misfires during reactivation to be reduced. For example, the exhaust valve of the reactivated cylinder may be opened during the exhaust stroke of the engine cycle immediately preceding the reactivation. In one example, the exhaust valve may be opened just before the start of the exhaust stroke. Thus, the exhaust valve may be opened later in the exhaust stroke, such as if a decision needs to be made later, however, the exhaust gas may have been compressed during the exhaust stroke, resulting in work when the exhaust valve is opened later Loss.

Optionally, at 318 , the valve operation of one or more other cylinders to be deactivated or remain activated may be adjusted in conjunction with the deactivation of the exhaust valves of the cylinders selected for deactivation in the next cycle. Therefore, various skip fire combinations can be produced. For example, when the first cylinder is normally fired and exhausted, the second cylinder may be configured to draw in air but not fuel, and discharge fresh charge. In yet another example, air from such a cylinder may be mixed with exhaust from other cylinders that is slightly richer than stoichiometric ratio to provide fuel and air to the catalyst to react and generate heat, resulting in rapid catalyst light-off. Other alternatives may include drawing in air and supplying fuel on the intake or compression stroke, but not providing spark, to produce an air-fuel mixture at the exhaust catalyst at the desired ratio. Additionally, the intake air may be compressed, but not fueled, until the exhaust stroke providing post injection. This can be combined with spark timing close to the exhaust event to provide combustion into the exhaust phase. This provides additional heat flux to the exhaust catalyst.

The choice between the different options can be based on NVH considerations and excitation pulses. For example, a rich burn event may add torque and/or torque pulses into the system. However, post injection in the exhaust stroke may only provide heat without a torque pulse into the system, thereby resulting in different NVH characteristics.

By simultaneously introducing known torque pulses into the engine system using the various combinations discussed at 318 , engine and exhaust catalyst temperatures may be better controlled while providing acceptable NVH characteristics. Additionally, activated cylinders can be operated without additional spark retard to add more heat flux to the exhaust catalyst. Since activated cylinders operate at higher average cylinder loads during selective cylinder deactivation, they may be more tolerant of additional spark retard.

As one example, the first cylinder may be selected for deactivation in cylinder mode. The first cylinder may have intake valve and/or exhaust valve operation disabled for a determined number of engine cycles. Additionally, a second, different cylinder may be selected for deactivation, for at least some of the determined number of engine cycles, at deactivated intake valves, deactivated exhaust valves, deactivated The second cylinder is operated with one or more of the fuel injectors and retarded spark.

As a non-limiting example, the engine controller may cause the second cylinder in a first mode in which the intake valve is open during the intake stroke, the fuel injectors are deactivated, the spark is deactivated, and the exhaust valve is open during the exhaust stroke run down. Alternatively, the engine controller may operate the second cylinder in a second mode in which the intake valve is open during the intake stroke, the fuel injectors are deactivated, the spark is deactivated, and the exhaust valve is open during the exhaust stroke . Alternatively, the engine controller may cause the second cylinder to have the intake valve open during the intake stroke or the compression stroke, the fuel injectors activated and fuel delivered during the compression stroke, the spark deactivated and the exhaust valve at the exhaust. Operates in a third mode turned on during the gas stroke. Alternatively, the engine controller may cause the second cylinder to be open during the fourth period in which the intake valve is open during the intake stroke, the fuel injector is activated, the spark is retarded to the exhaust stroke, and the exhaust valve is open during the exhaust stroke. operating in the mode. Thus, various combinations of valve, fuel, and spark adjustments achieve different amounts of heat to be transferred to engine components. It should be appreciated that other modes than those listed above are possible to provide a combination of valve, fuel and spark adjustments that deliver the desired heat to the engine (eg, cylinders, exhaust catalysts, etc.). The controller may further select the operating mode for the second cylinder based on the engine temperature.

Therefore, the controller may target heating the catalyst or heating the engine/engine cylinders. In one example, the controller may respond to the second cylinder requiring more heating than the first cylinder (such as when combustion does not occur in the second cylinder for a certain duration, or when the cooling system is deregulated) or in response to The second cylinder is connected to a different catalyst than the first cylinder (such as in a V-engine configuration) and a mode other than the first mode (such as the second mode, the third mode, or the fourth mode is selected) a), where the catalyst coupled to the second cylinder requires additional heating to be fully activated.

As yet another example, when operating the engine cylinders in the selected cylinder mode of the deactivated/activated cylinders, the controller may cause at least one of the remaining cylinders to be spark activated and fuel rich (eg, via relative to operating with stoichiometric rich fuel injection delivered during the compression stroke) while at least one other of the remaining cylinders is spark activated and fuel lean (eg, via relative stoichiometric fuel injection delivered during the compression stroke) Lean fuel injection) to raise the engine temperature above the threshold. In this context, the rich cylinders will provide some CO and hydrocarbons at the catalyst that will react with the oxygen provided to the catalyst through the lean cylinders. In this way, the rich charge from the enriched cylinder may be mixed with the lean charge from the leaner cylinder at the engine exhaust, such as at the exhaust catalyst, thereby producing an exothermic reaction at the catalyst . Therefore, this accelerates exhaust catalyst heating.

In yet another example, when operating the engine cylinders in the selected cylinder mode of the deactivated/activated cylinders, the controller may cause at least one of the remaining cylinders to be stoichiometrically stoichiometric when spark is deactivated Operates with fuel supplied to accelerate catalyst heating.

Turning now to FIG. 4 , map 400 illustrates example exhaust valve adjustments for a four-cylinder in-line engine having cylinders 1-4 arranged in series along a cylinder block (not shown). Cylinders 1-4 are configured to fire in the sequence 1-3-4-2. Map 400 depicts intake valve timing (solid lines) and exhaust valves with respect to engine piston position on the intake stroke (I), exhaust stroke (E), power stroke (P) or compression stroke (C) Timing (dotted line). Map 400 further depicts cylinder spark ignition events with asterisks 403a-b, 413b, 423a-b, 433a-b and cylinder fuel injection events with rectangles 402a-b, 412b, 422a-b, 432b.

In the depicted example, in the first cycle (Cycle_1), the engine fires in a firing sequence 1-3-4-2, where each cylinder of the engine fires once. Then, on the next cycle (Cycle_2), skip fire mode is entered and the engine fires according to the cylinder pattern 1-x-4-x, where x represents the cylinder being skipped. Here, each alternate cylinder is fired and the other alternate cylinder is skipped, resulting in a 1/2 firing pattern. In this case, the firing of cylinder 3 is skipped after the firing of cylinder 1, and then the firing of cylinder 2 is skipped after the firing of cylinder 4.

The first graph from the top of the figure represents the position of cylinder number 1 (cylinder 1). And, specifically, the stroke of the No. 1 cylinder follows the rotation of the engine crankshaft. Cylinder 1 strokes are marked according to engine position. For example, cylinder 1 is shown first on the intake stroke (I), the engine spins, and cylinder number 1 enters the compression stroke (C) followed by the power (P) stroke and exhaust (E) stroke. The cylinder cycle for cylinder 1 then repeats. For a four-stroke engine, the cylinder cycle may be 720°, with the same crankshaft spacing for the entire cycle of the engine.

Likewise, the second graph from the top of the figure represents the position of cylinder number 3 (cylinder 3), specifically the stroke of cylinder number 3 as the engine crankshaft rotates. Cylinder 3 strokes are marked according to engine position. For example, cylinder 3 is shown first on the exhaust stroke (E), the engine spins, and cylinder number 3 enters the intake stroke (I) followed by the compression (C) and power (P) strokes. The cylinder is then deactivated for the next combustion cycle, which will begin on the subsequent intake stroke. Likewise, the third graph from the top of the figure represents the position of cylinder number 4 (cylinder 4), specifically the stroke of cylinder number 4 as the engine crankshaft rotates. Cylinder 4 strokes are marked according to engine position. For example, cylinder 4 is shown first on the power stroke (P), the engine spins, and cylinder number 4 enters the exhaust stroke (E) followed by the intake (I) stroke and compression (C) stroke. The cylinder cycle for cylinder 4 then repeats. Likewise, the fourth graph from the top of the figure represents the position of cylinder number 2 (cylinder 2), specifically the stroke of cylinder number 2 as the engine crankshaft rotates. Cylinder 2 strokes are marked according to engine position. For example, cylinder 2 is shown first on the compression stroke (C), the engine spins, and cylinder number 2 enters the power stroke (P) followed by the exhaust (E) and intake (I) strokes. This cylinder is then deactivated for the next combustion cycle (Cycle_2).

With reference to the first cylinder, a first cylinder event is shown at 401a-404a, and a subsequent cylinder event in cylinder 1 is shown at 401b-404b. During each of the first and second cylinder events, the intake valve is opened (401a, 401b) during the intake stroke to provide air to the cylinder. Fuel is then injected into the engine cylinders (402a, 402b) through port injectors or direct injectors. The fuel and air mixture is compressed and ignited during the compression stroke (403a, 403b). Peak cylinder pressure may occur at top dead center of the compression stroke or during the expansion stroke. Exhaust gas is then released by opening the exhaust valve during the exhaust stroke (404a, 404b). Herein, exhaust valve operation at 404a continues as desired since cylinder 1 is to remain activated after the first cylinder event.

Referring to the fourth cylinder, the end of the first cylinder event is shown at 423a-424a, and the subsequent cylinder event in cylinder 4 is shown at 421b-424b. During each of the first and second cylinder events, the intake valve is opened during the intake stroke (421b shown) to provide air to the cylinder. Fuel is then injected into the engine cylinders (422b shown) through port injectors or direct injectors. The fuel and air mixture is compressed and ignited during the compression stroke (423a, 423b). Peak cylinder pressure may occur at top dead center of the compression stroke or during the expansion stroke. Exhaust gas is then released by opening the exhaust valve during the exhaust stroke (424a, 424b). Here, as with cylinder 1, exhaust valve operation at 424a continues as desired since cylinder 4 is to remain activated after the first cylinder event. Again, since cylinder 4 is to remain activated after the second cylinder event, exhaust valve operation at 424b continues as desired and is followed by another intake valve and fuel event at 421c and 422c, respectively.

Referring to the third cylinder, the first cylinder event is shown at 411b-413b, and at the subsequent cylinder event (ie, during Cycle_2), cylinder 3 is deactivated. Specifically, each of the fuel, spark, and valve operation of cylinder 3 is deactivated for the cylinder events following 411b-413b. During the first cylinder event (ie, during Cycle_1), the intake valve is opened (411b) during the intake stroke to provide air to the cylinder. Fuel is then injected into the engine cylinders ( 412b ) through port injectors or direct injectors. The fuel and air mixture is compressed and ignited during the compression stroke (413b). Peak cylinder pressure may occur at top dead center of the compression stroke or during the expansion stroke. However, since cylinder 3 is to be deactivated after the first cylinder event, the exhaust is not released, but is instead held in the cylinder by keeping the exhaust valve closed during the exhaust stroke. In contrast, the cylinder event prior to the first cylinder event shown at 411b-413b, exhaust valve operation at 414a is allowed to continue with the exhaust valve open on the exhaust stroke to release exhaust gas. By closing the exhaust valve at a cylinder event in Cylinder 3 (in Cycle_1) prior to the deactivation of Cylinder 3 (in Cycle_2), heat is retained in the combustion chamber, allowing heating of the combustion surfaces of the cylinder, and by This reduces the release of PM emissions when cylinder 3 is subsequently reactivated. Additionally, coolant temperature may be increased (eg, slowly) for engine standstill to improve passenger comfort.

Likewise, with reference to the second cylinder, a first cylinder event is shown at 431b-433b, and on a subsequent cylinder event, cylinder 2 is deactivated. Specifically, each of the fuel, spark, and valve operation of cylinder 2 is deactivated for the cylinder events following 431b-433b. During the first cylinder event, the intake valve is opened (431b) during the intake stroke to provide air to the cylinder. Fuel is then injected into the engine cylinders (432b) through port injectors or direct injectors. The fuel and air mixture is compressed and ignited during the compression stroke (433b). Peak cylinder pressure may occur at top dead center of the compression stroke or during the expansion stroke. However, since cylinder 2 is to be deactivated after the first cylinder event, the exhaust is not released, but is instead held in the cylinder by keeping the exhaust valve closed during the exhaust stroke. In contrast, for the cylinder event prior to the first cylinder event shown at 431b-433b, exhaust valve operation at 434a is allowed to continue with the exhaust valve open on the exhaust stroke to release exhaust gas. By closing the exhaust valve at a cylinder event in cylinder 2 prior to deactivation of cylinder 2, heat is retained in the combustion chamber, allowing heating of the combustion surfaces of the cylinder and thereby reducing PM emissions when cylinder 2 is subsequently reactivated release.

It should be appreciated that when cylinders 2 and 3 are subsequently reactivated, the exhaust valves of the reactivated cylinders may be opened before the intake valve(s) are opened to allow for remaining trapped in the cylinders Any residual gas in the air is pushed out before the fresh charge is drawn into the cylinder. This allows the occurrence of misfires during reactivation to be reduced. For example, in response to an indication for cylinder reactivation, the exhaust valve of the deactivated cylinder may be opened on the exhaust stroke of the engine cycle immediately preceding the reactivation to expel the residue. The cylinders may then be reactivated, and the intake and exhaust valves may operate as desired during the intake and exhaust strokes, respectively. In other words, the exhaust valve of the deactivated cylinder is opened during the exhaust stroke immediately before reactivation, and then opened during the exhaust stroke after reactivation.

An example method for an engine includes: selecting a cylinder for deactivation; and maintaining an exhaust valve of the selected cylinder closed during an exhaust stroke of the cylinder immediately prior to the engine cycle prior to deactivation. In the above examples, additionally or alternatively, the cylinders selected for deactivation are responsive to a drop in engine load. In any or all of the above examples, the exhaust gas temperature is additionally or alternatively above the threshold temperature during the selection period. Any or all of the above examples may additionally or alternatively further include, during reactivation of the selected cylinder, opening the exhaust valve prior to opening the intake valve to release trapped exhaust prior to intake air. gas. In any or all of the above examples, opening the exhaust valve may additionally or alternatively include opening the exhaust valve during the exhaust stroke of the engine cycle immediately preceding reactivation. In any or all of the above examples, the selected cylinder is the first cylinder, and the method may additionally or alternatively further comprise, selecting a second, different cylinder for deactivation, and deactivating the second cylinder Operates with one or more of a deactivated intake valve, a deactivated exhaust valve, a deactivated fuel injector, and a retarded spark. In any or all of the above examples, the operating may additionally or alternatively include causing the second cylinder to open during the intake stroke, the fuel injectors to be deactivated, the spark to be deactivated, and The exhaust valve is operated in the first mode during the exhaust stroke; the second cylinder is caused to have the intake valve open during the intake stroke, the fuel injectors are deactivated, the spark is deactivated and the exhaust valve is open during the exhaust stroke Operates in a second mode that is open during the period; having the second cylinder open with the intake valve open during the intake or compression stroke, the fuel injectors activated and fuel delivered during the compression stroke, the spark deactivated and the exhaust valve at Operates in third mode open during exhaust stroke; second cylinder with intake valve open during intake stroke, fuel injector activated, spark retarded to exhaust stroke and exhaust valve open during exhaust stroke operating in a fourth mode of ; and selecting the mode based on the exhaust catalyst temperature. Any or all of the above examples may additionally or alternatively further include deactivating selected cylinders for a plurality of engine cycles, wherein maintaining the exhaust valves of the selected cylinders closed in response to a high number of engine cycles at the threshold times. In any or all of the above examples, additionally or alternatively, the threshold number of times is based on one or more of engine coolant temperature, ambient temperature, and cylinder temperature, the threshold number being a function of engine coolant temperature, decreases as any one of ambient temperature and cylinder temperature decreases.

Another example method for an engine includes deactivating a cylinder mode of an individual cylinder mechanism, the cylinder mode including a first deactivated cylinder and a second activated cylinder, wherein in response to a command for deactivation of the first cylinder, And further based on engine temperature, the exhaust valve of the first cylinder is held closed for the exhaust stroke of the engine cycle immediately prior to deactivation of the first cylinder. In the above example, additionally or alternatively, the exhaust valve of the first cylinder may be held closed in response to the engine temperature being below a threshold. In any or all of the above examples, the cylinder mode may additionally or alternatively further include the number of engine cycles during which the first cylinder is maintained deactivated, and the method may additionally or alternatively further include , the first cylinder is reactivated after the number of engine cycles. In any or all of the above examples, additionally or alternatively, the engine temperature is an estimated engine temperature or a desired engine temperature, the desired engine temperature including the desired engine or engine component temperature upon reactivation. Any or all of the above examples may additionally or alternatively further include, during reactivation, opening the exhaust valve of the first cylinder prior to opening the intake valve of the first cylinder to allow air to be drawn into the first cylinder Before releasing the trapped exhaust. Any or all of the above examples may additionally or alternatively further include, in response to the desired engine temperature being below a threshold, enabling the third cylinder to be delivered with rich fuel injection and spark deactivated during the compression stroke The fourth cylinder is operated with lean fuel injection delivered during the intake stroke and spark deactivated.

Another example engine system includes an engine having a plurality of cylinders, each cylinder including an intake valve and an exhaust valve; a deactivation mechanism for deactivating the intake and exhaust of one of the plurality of cylinders at least one of the doors; a temperature sensor for estimating engine temperature; and a controller. The controller may be configured with computer readable instructions stored on non-transitory memory for: selecting one of the plurality of cylinders for deactivation based on engine load; and In the first engine cycle, the intake valve of each of the plurality of engine cylinders is opened during the corresponding intake stroke, the exhaust valve of one of the plurality of cylinders is kept closed during the exhaust stroke, and the corresponding opening the exhaust valves of the remaining cylinders during the exhaust stroke; and in the second engine cycle, immediately after the first engine cycle, deactivating the intake and exhaust valves of one of the plurality of cylinders while maintaining the remaining cylinders activation. In the above examples, maintaining the exhaust valve of one of the plurality of cylinders closed during the exhaust stroke may additionally or alternatively be in response to the engine temperature being below a threshold. Any or all of the above examples may additionally or alternatively further include operating one or more of the remaining cylinders with spark timing retarded into the exhaust stroke to increase engine temperature above the threshold. Any or all of the above examples may additionally or alternatively further include operating at least one of the remaining cylinders with spark activation and fuel enrichment while operating at least one of the remaining cylinders with spark activation and fuel enrichment. Operates fuel lean to raise engine temperature above a threshold. Any or all of the above examples may additionally or alternatively further include, during the third engine cycle, reactivating and opening the exhaust valve of one of the plurality of cylinders during the exhaust stroke, and During the fourth engine cycle immediately following the third engine cycle, the intake valve of one of the plurality of cylinders is reactivated and opened during the intake stroke.

In a further representation, a method for an engine includes deactivating a cylinder mode of an individual cylinder mechanism, the cylinder mode a first deactivated cylinder and a second activated cylinder, wherein in response to a cylinder mode for the first cylinder The deactivation command, the exhaust valve of the first cylinder is held closed for the exhaust stroke of the ignition cycle immediately preceding the deactivation of the first cylinder.

In this way, the technical effect of maintaining exhaust from combustion in deactivated cylinders is that the deactivation benefits can be extended for longer durations without degrading exhaust emissions. By keeping the exhaust valve of the cylinder to be deactivated in the next cycle closed during the exhaust stroke, hot exhaust gas can be held in the cylinder, boosting combustion of the deactivated cylinder even when the cylinder is deactivated surface temperature. Thus, this not only reduces the need for cold cylinder reactivation, thereby improving fuel economy, but also reduces particulate matter emissions from the reactivated cylinders. By also selectively operating the activated cylinder with variable valve and spark operation when other cylinders of the cylinder pattern are deactivated, exhaust catalyst warming is accelerated and the duration of engine operation with cylinder deactivation is extended. This allows the fuel economy benefits of cylinder deactivation to be prolonged, thereby improving engine performance and fuel economy.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and programs disclosed herein may be stored as executable instructions in non-transitory memory and may be implemented by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific procedures described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, the various acts, operations and/or functions described may be performed in the order shown, in parallel, or in some cases omitted. Likewise, the described order of processing is not necessarily required to implement the features and advantages of the example embodiments of the invention described herein, but is provided for ease of illustration and description. Depending on the particular strategy used, one or more of the illustrated actions, operations, and/or functions may be repeatedly performed. Additionally, the described acts, operations, and/or functions may graphically represent code programmed into a non-transitory memory of a computer-readable storage medium in an engine control system, where executed in cooperation with an electronic controller, including various engine hardware components The described actions are carried out by the instructions in the system.

It should be appreciated that the configurations and procedures disclosed herein are exemplary in nature and that these specific examples are not to be considered limiting, as many variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4 and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations and other features, functions and/or properties disclosed herein.

The claims of this application particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

Claims (15)

1. A method for an engine comprising: selection of the first cylinder for deactivation; maintaining the exhaust valve of the selected cylinder closed during the exhaust stroke of the cylinder for the engine cycle immediately preceding the deactivation; select a different second cylinder for deactivation, operating the second cylinder in a first mode in which the intake valve is open during the intake stroke, the fuel injectors are deactivated, the spark is deactivated, and the exhaust valve is open during the exhaust stroke; A second cylinder having the intake valve open during the intake stroke, the fuel injector activated, spark deactivated, and the exhaust valve open during the exhaust stroke run in mode; having the second cylinder open during the intake or compression stroke, the fuel injector activated and fuel delivered during the compression stroke, spark deactivated and the exhaust operating in a third mode with the valve open during the exhaust stroke; causing the second cylinder to open during the intake stroke, the fuel injector activated, spark retarded to the exhaust stroke and the exhaust valve to be open during the exhaust stroke operating in the fourth mode turned on during the period; and One of the modes is selected based on the exhaust catalyst temperature. 2 . The method of claim 1 , wherein the cylinders selected for deactivation are responsive to a drop in engine load. 3 . 3. The method of claim 1, wherein during the selecting, an exhaust gas temperature is above a threshold temperature. 4. The method of claim 1, further comprising: during reactivation of the selected first cylinder, opening the exhaust valve prior to opening an intake valve to release trapped prior to intake air of exhaust. 5. The method of claim 4, wherein opening the exhaust valve comprises opening the exhaust valve during an exhaust stroke of an engine cycle immediately preceding the reactivation. 6 . The method of claim 1 , further comprising: deactivating the selected first cylinder for a number of engine cycles, wherein the maintaining an exhaust valve of the selected first cylinder is closed in response to 6 . The number of engine cycles is above a threshold number. 7 . The method of claim 6 , wherein the threshold number is based on one or more of engine coolant temperature, ambient temperature, and cylinder temperature, the threshold number varying with the engine coolant temperature, the ambient temperature, and the decreases with a decrease in either of the temperature and the cylinder temperature. 8. A method for an engine comprising: deactivating a cylinder pattern of an individual cylinder mechanism, the cylinder pattern including a first deactivated cylinder and a second activated cylinder, wherein in response to a command for deactivation of the first cylinder, and further based on engine temperature, the exhaust valve of the first cylinder is held closed for an exhaust stroke of an engine cycle immediately prior to the deactivation of the first cylinder; and In response to the engine temperature being below the threshold, the third cylinder is operated with rich fuel injection delivered during the compression stroke and spark is deactivated, while the fourth cylinder is operated with lean fuel injection during the intake stroke Operates with delivery and spark deactivated. 9 . The method of claim 8 , wherein the exhaust valve of the first cylinder being held closed based on an engine temperature comprises the exhaust valve being held closed in response to the engine temperature being below the threshold. 10 . 10. The method of claim 9, wherein the cylinder pattern further comprises a number of engine cycles during which the first cylinder is maintained deactivated, the method further comprising: after the number of engine cycles The first cylinder is reactivated. 11. The method of claim 10, wherein the engine temperature is an estimated engine temperature or a desired engine temperature, the desired engine temperature including the desired temperature of the engine or engine component at the reactivation . 12. The method of claim 10, further comprising, during the reactivation, opening the exhaust valve of the first cylinder prior to opening the intake valve of the first cylinder to The trapped exhaust gas is released before air is drawn into the first cylinder. 13. An engine system comprising: an engine having a plurality of cylinders, each cylinder including an intake valve and an exhaust valve; a deactivation mechanism for deactivating at least one of the intake valve and the exhaust valve of one of the plurality of cylinders; a temperature sensor for estimating engine temperature; and a controller configured with computer readable instructions stored on non-transitory memory for: selecting one of the plurality of cylinders for deactivation based on engine load; and During a first engine cycle, the intake valve of each of the plurality of engine cylinders is opened during a corresponding intake stroke, and the intake valve of one of the plurality of cylinders is held during an exhaust stroke the exhaust valve is closed while the exhaust valve of the remaining cylinders is opened during the corresponding exhaust stroke; and in a second engine cycle, immediately after the first engine cycle, deactivating the intake valve and the exhaust valve of the one of the plurality of cylinders while maintaining activation of the remaining cylinders; wherein maintaining the exhaust valve of the one of the plurality of cylinders closed during the exhaust stroke is responsive to the engine temperature being below a threshold, the computer readable instructions are further for: causing the At least one of the remaining cylinders is operated spark-activated and fuel-enriched, while at least another of the remaining cylinders is operated spark-activated and fuel-lean to raise the engine temperature to a desired above the threshold. 14. The system of claim 13, the computer readable instructions further for: operating one or more of the remaining cylinders with spark timing retarded into an exhaust stroke to enable The engine temperature rises above the threshold. 15. The system of claim 13, the computer readable instructions further for: reactivating the exhaust of the one of the plurality of cylinders during an exhaust stroke during a third engine cycle valve and open the exhaust valve, and reactivate the intake valve of the one of the plurality of cylinders during an intake stroke during a fourth engine cycle immediately following the third engine cycle and open the intake valve.

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